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THE  CONDUCTIVITY  OF  AIR  CAUSED  BY 
CERTAIN  CHEMICAL  CHANGES 


THESIS 

Presented  to  the  Faculty  of  Philosophy  of  the   University  of 

Pennsylvania  In  partial  fulfilment  of  the  requirements 

for  the  degree  of  Doctor  of  Philosophy 


S,irtHA7*7 

f    UNIVERSITY    } 


BY 
FAXXY  COOK   GATES 


1909 


THE  CONDUCTIVITY  OF  AIR  CAUSED  BY  CERTAIN 
CHEMICAL  CHANGES. 

THE  ionization  of  gases  is  the  accompaniment  of  a  large  number  of 
phenomena  which  are  apparently  of  totally  different  character  and 
origin.  Many  of  these  phenomena  have  been  studied  with  consider- 
able care  and  have  already  thrown  much  light  on  the  nature  of  elec- 
trical charges,  and  have  brought  forward  more  satisfactory  hypotheses 
regarding  the  constitution  of  matter  than  had  previously  existed.  Of 
other  phenomena  with  which  seem  to  be  associated  the  ionization  of 
gases,  very  little  is  known;  and  particularly  has  this  been  the  case 
when  the  ionization  occurs  during  chemical  changes  in  neighboring 
substances. 

G.  Le  Bon  first  noted  that  when  the  sulphate  of  quinine  was  heated 
or  cooled,  the  air  about  it  was  made  a  conductor  of  electricity  and  that 
at  the  same  time  a  phosphorescent  glow  was  observed  over  the  entire 
surface  of  the  quinine.  He  attributed  these  effects  to  the  hydration 
and  dehydration  known  to  accompany  the  temperature  changes 
during  which  the  effects  were  noted  and  advanced  this  as  an  argument 
for  believing  that  the  conductivity  of  gases  in  the  presence  of  radio- 
active substances,  is  due  to  chemical  processes  resulting  from  tempera- 
ture changes  within  the  body. 

For  the  purpose  of  refuting  or  establishing  this  deduction,  the  author 
made  a  comparative  study1  of  the  radiations  from  quinine  sulphate 
under  the  conditions  described,  with  those  from  thorium  and  radium, 
and  found  the  two  to  be  wholly  unlike;  the  former  showing  every 
indication  that  the  discharge  of  the  air  condenser  used,  was  due  to  the 
ionization  of  the  gas,  while  in  the  case  of  the  radio-active  substances, 
the  discharge  was  produced  by  the  projection  of  charged  particles 
from  the  substance.  The  exact  effects  of  cooling  quinine  through 
different  intervals  of  temperature  were  carefully  noted  with  the  result 
that  the  greatest  conductivity  of  the  air  in  each  case  was  found  to  take 
place  during  the  temperature  change  and  rate  of  change,  in  which 
hydration  was  a  maximum. 

LeBon  makes  the  statement  that  except  for  the  sulphate  of  cin- 
chonine,  a  substance  very  similar  to  quinine,  no  substance  could  be 
found  which  gave  similar  effects;  but  he  does  not  tell  what  substances 
were  tested  and  his  statement  is  therefore  of  little  value. 

Kalahne  made  an  interesting  study  of  the  quinine  radiations, 
described  in  the  Annalen  for  November,  1905,  in  which  he  concerned 

1  Physical  Review,  May,  1904. 

202475 


himself  with  testing  the  relative  effects  during  heating  and  cooling; 
the  relative  conductivities  produced  in  air,  hydrogen  and  carbon 
dioxide  by  the  same  amount  of  quinine;  the  maximum  amount  of 
water  which  a  unit  mass  of  quinine  sulphate  can  hold;  and  the  effect 
of  vapor  pressure  and  temperature  on  dissociation  pressure.  He  also 
found,  as  did  the  author,  that  cooling  dry  heated  quinine  in  dry  air 
gives  neither  ionization  nor  light,  but  that  both  begin  with  the  intro- 
duction of  damp  air. 

The  work  described  in  the  present  paper  was  undertaken  with  the 
hope  of  ascertaining  more  facts  regarding  the  cause  as  well  as  the 
nature  of  the  quinine  radiation;  whether  it  is  always  accompanied  by 
phosphorescence  and  if  so,  whether  the  electrical  effect  may  not  be  due 
to  it,  rather  than  to  the  hydration  or  dehydration  alone;  and  whether 
other  substances  can  be  found  which  give  similar  effects.  An  abstract 
of  some  preliminary  observations  appeared  in  the  Physical  Review 
for  January,  1906.  Since  then,  the  work  has  been  continued  in  the 
Cavendish  Laboratory,  and  the  writer  takes  this  opportunity  of 
expressing  her  appreciation  of  the  courtesy  extended  by  Professor 
Thomson  in  placing  the  facilities  of  the  laboratory  at  her  disposal  and 
of  his  interest  shown  during  the  progress  of  the  work. 

The  question  as  to  what  effect,  if  any,  the  phosphorescence  may 
have  upon  the  conductivity  of  the  air  is  a  most  important  one  to  con- 
sider. If  the  phosphorescence  is  the  cause  of  the  conductivity,  one 
reasonable  explanation  would  seem  to  be  that  the  latter  is  due  to  the 
presence  of  short  ultraviolet  light  waves  accompanying  the  phosphor- 
escence, such  as  Lenard  has  shown  to  cause  ionization  when  they 
strike  a  negatively  charged  surface.  The  only  apparent  difference 
between  this  case  and  that  which  Lenard  describes  is  that  with  quinine, 
the  ionization  takes  place  whether  the  plate  on  which  the  quinine  rests, 
is  charged  positively  or  negatively.  This  seemed  to  exclude  the 
ultraviolet  light  theory,  until  it  was  found  that  the  intensity  of  the 
ionization  current  was  always  greater  when  the  quinine  was  placed  on 
the  positive  rather  than  the  negative  plate  of  the  condenser.  This 
fact  would  tend  to  explain  the  effect  by  considering  that  when  the 
lower  plate  is  positive  the  light  strikes  the  upper  negatively  charged 
plate  and  ionization  follows;  when,  however,  the  upper  plate  is  posi- 
tive, the  ionization  is  produced  only  after  the  light  has  been  reflected 
by  the  upper  to  the  lower  negatively  charged  plate,  in  which  case  some 
of  the  energy  would  be  necessarily  dissipated.  The  ratio  of  the 
intensity  of  the  ionization  current  in  these  two  cases  when  the  plates 
are  separated  by  2  cm.  of  air  is  1.6,  and  increases  rapidly  as  the  air 
space  is  increased,  being  2.5  when  the  plates  are  7  cm.  apart.  This  is 
what  would  be  expected  if  the  above  explanation  is  the  correct  one. 

Le  Bon  declared  that  the  conductivity  of  the  gas  could  not  be  due 
to  the  phosphorescence  since  the  latter  persists  longer  than  the  former. 


The  author  found  this  statement  not  true,  but  that  the  ionization  con- 
tinued long  after  the  phosphorescence  had  ceased  to  be  visible,  when 
tested  near  the  surface  of  the  quinine.  This  might  be  equally  well 
claimed  as  an  argument  against  the  ultraviolet  light  theory  unless  we 
can  assume  the  presence  of  the  short  ultraviolet  waves  after  the  longer 
visible  waves  have  ceased,  both,  however,  having  a  common  cause. 
Much  stronger  would  be  the  evidence  against  the  theory  if  conditions 
could  be  found  under  which  ionization  takes  place  without  a  trace  of 
phosphorescence,  or  at  least  conditions  in  which  a  variation  in  the 
magnitude  of  one  effect  is  not  accompanied  by  a  corresponding  change 
in  the  other  effect. 

Tests  were  first  made  to  determine  what  effect  a  reduction  of  pressure 
would  have  on  the  ionization  current.  That  entire  exclusion  of  air 
and  moisture  would  cause  the  effects  to  cease  was  to  have  been 
expected,  and  the  behavior  at  merely  comparatively  low  pressures 
was,  therefore,  of  greatest  interest.  For  these  observations  two  types 
of  testing  chambers  were  used :  with  one,  the  quinine  was  first  heated 
in  the  outside  air  and  cooled  under  cover  at  lowered  pressure;  while 
with  the  other,  the  heating  took  place  inside  the  testing  vessel  itself 
and  at  a  low  pressure.  The  first  apparatus  was  made  as  follows:  A 
circular  block  of  ebonite  1 .5  cm.  thick  was  used  as  a  base,  and  on  its 
upper  surface  at  regular  intervals  were  glued  three  small  blocks  to  sup- 
port the  metal  plate,  over  which  the  quinine  was  spread.  A  short  stiff 
wire  was  soldered  to  the  lower  side  of  this  metal  plate,  and  was  just  long 
enough  to  dip  into  a  few  drops  of  mercury  contained  in  a  small  cup- 
like  depression  in  the  centre  of  the  base.  In  this  way,  by  means  of  a 
fine  sealed  wire  piercing  through  the  base,  electrical  contact  was  made 
between  the  terminal  of  a  battery  without,  and  the  plate  on  which  the 
quinine  was  spread,  wrhen  the  latter  was  under  cover.  The  upper  por- 
tion of  the  apparatus  consisted  of  a  cylindrical  brass  cover  10  cm.  in 
diameter  and  5  cm.  high.  A  metal  plate  the  size  of  the  one  on  which 
the  quinine  rested,  was  screwed  on  the  end  of  a  brass  rod  piercing  an 
ebonite  stopper  in  the  centre  of  the  cover.  By  means  of  this  rod,  this 
plate  could  be  raised  or  lowered  to  any  desired  distance  above  the  sur- 
face of  the  quinine.  To  the  upper  outside  end  of  the  rod  was  attached 
a  wire  connecting  it  with  a  C.  T.  R.  Wilson  electroscope.  The  cover  to 
the  above  apparatus  was  made  to  fit  over  rubber  packing  in  a  circular 
trough  cut  in  the  ebonite  base.  After  heating  the  plate  containing  the 
quinine  and  placing  it  in  position  in  this  chamber,  weights  were  put  on 
top  of  the  cover  and  mercury  was  poured  into  the  outside  of  the  trough 
to  insure  an  air-tight  apartment.  (Fig.  1.) 

One-half  of  a  gram  of  quinine  sulphate  was  sifted  uniformly  over 
the  metal  plate  of  the  above  apparatus  and  heated  to  180°  C.  in  an 
air  bath.  It  was  then  quickly  placed  in  position  in  this  apparatus  and 
joined  to  the  positive  terminal  of  a  2CO-volt  battery.  \Yith  the  upper 


plate  2  cm.  distant  and  joined  to  an  electroscope  in  which  a  deflection 
of  one  division  per  second  was  found  to  be  caused  by  a  discharging 
current  of  the  order  of  10~13  amperes,  when  tested  directly  in  con- 


FIG.  1. 


To  Electroscope 


Exhaust 


To  Battery 


nection  with  a  condenser  of  known  capacity,  the  following  readings 
were  obtained  from  the  quinine  at  atmospheric  pressure.  Curve  A 
shows  the  current-time  variation  for  the  same. 


%  READINGS  FOR  CURVE  A,  ATMOSPHERIC  PRESSURE. 


Time  after 

heating. 
1  min.  30  sec. 


4 
27 
52 

14 
40 

7 
4 


Current  in 

arbitrary  unit. 

Began 

37.5 

75.0 

75.0 

43.0 

29.0 

20.0 

12.5 


Time  after 

heating. 
5  min.  35  sec. 


6 

7 

8 

9 

10 

12 


17 

9 
22 

30 
46 
20 


Current  in 

arbitrary  unit. 

10.0 

7.0 

5.5 

4.5 

3.4 

3.0 

2.6 


EFFECT  OF  PRESSURE. 

With  exactly  the  same  conditions  except  that  the  cooling  took  place 
under  reduced  pressures  of  10  cm.  and  3  cm.  respectively,  curves 
B  and  C  were  obtained.  (Fig.  2.)  When  lower  pressures  were  used, 
however,  it  was  found  that  the  ionization  current  rapidly  decreased. 


This  is  presumably  due  to  the  fact  that  at  lower  pressures  the  remain- 
ing air  in  the  chamber  contained  insufficient  moisture  to  produce  the 
normal  effect. 

FIG.  2. 


3o 


It  is  of  interest  to  note  that  except  for  the  time  at  which  the  ioniza- 
tion  current  is  first  detected,  curves  B  and  C  are  almost  identical  with 
those  produced  at  atmospheric  pressure,  when  the  distances  between 
plates  are  greatly  decreased.  Thus,  it  would  seem  that  the  strength 
of  the  ionization  current  depends  upon  the  amount  of  air  between 
the  plates,  and  can  be  increased  by  either  decreasing  the  distance 
between  plates  or  by  lowering  the  pressure.  The  difference  in  behavior 


at  the  beginning  of  the  effect  may  be  explained  by  considering  either 
that  the  lower  pressure  changes  the  rate  of  cooling,  or  that  in  the  case 
of  the  rarer  air,  a  longer  time  is  required  for  the  quinine  to  receive 
sufficient  moisture  to  start  the  effect. 

To  test  the  effect  of  pressure  on  the  rate  of  cooling,  one  terminal  of 
a  thermopile  was  placed  between  the  plates,  while  the  other  terminal 
was  kept  without  in  a  constant  temperature  bath.  Differences  in 
temperature  within  and  without  were  measured  during  the  cooling 
of  quinine  at  atmospheric  pressure  and  again  at  a  pressure  of  3  cm. 
respectively.  Although  the  galvanometer  was  sufficiently  sensitive  to 
record  changes  of  .05  C.,  the  rate  of  cooling  was  found  not  to  be  appre- 
ciably different  in  the  two  cases,  it  requiring  ten  minutes  for  the  tem- 
perature within  to  be  reduced  to  that  of  the  room  outside. 

In  order  to  determine  whether  the  effects  on  the  ionization  brought 
about  by  changes  in  pressure  were  in  each  case  accompanied  by  a 
similar  change  in  the  phosphorescence,  a  mica  window  was  inserted  in 
the  side  of  the  apparatus  and  all  of  the  above  described  tests  were 
repeated  in  a  dark  room.  These  tests  showed  that  with  every  decrease 
in  ionization  there  was  a  corresponding  decrease  in  phosphorescence, 
and  vice  versa. 

In  all  of  these  experiments  the  heating  of  the  quinine  took  place  in  a 
different  air  chamber  from  that  in  which  it  was  finally  tested.  In 
order  to  determine  what  effect  was  due  to  the  contact  of  the  hot 
quinine  with  the  outside  air  during  its  removal  from  the  oven  to 
the  testing  vessel,  experiments  were  made  similar  to  those  already 
described,  except  that  in  these,  the  heating  took  place  within  the 
testing  vessel  itself.  For  this  purpose,  the  above  apparatus  was  modi- 
fied by  the  introduction  of  two  openings  in  opposite  sides  of  the  cylin- 
drical cover.  These  openings  were  plugged  with  ebonite  stoppers 
through  which  stout  copper  rods  were  inserted,  holding  in  place  a 
thick  sheet  of  platinum  foil  to  which  each  was  welded.  The  quinine 
was  sprinkled  over  the  sheet  of  platinum  and  a  heating  current  was 
sent  across  it.  In  the  case  when  the  pressure  was  lowered  before  the 
heating  took  place,  the  conductivity,  as  shown  by  the  discharge  of  the 
electroscope,  took  place  as  before;  but  no  effect  was  obtained  upon 
cooling,  in  the  case  when  the  exhaustion  had  been  in  progress  during 
the  heating.  This  again,  might  have  been  predicted  if  we  had  regarded 
the  ionization  as  due  to  hydration,  since  in  the  first  case,  the  moisture 
thrown  off  during  heating  was  re-absorbed  upon  cooling,  while  in  the 
second  case,  it  was  pumped  out  as  soon  as  it  was  given  up  by  the 
quinine. 


EFFECT  OF  A  MAGNETIC  FIELD. 

Tests  were  made  for  the  purpose  of  determining  whether  the  pres- 
ence of  a  magnetic  field  would  change  the  ionization  current.  The 
testing  vessel  was  placed  between  the  poles  of  a  powerful  electro- 
magnet and  the  following  readings  taken  during  the  cooling  of  quinine 
under  7  cm.  pressure,  with  and  without  the  presence  of  the  magnetic 
field. 


Time.  Current. 
11  hr.  7  min.  35  sec.  60 

8  30  42.2 

8  50  37.50 

9  50  30 
12           30  17 


Magnetic  field. 
Off 
On 
Off 
On 
Off 


These  readings  give  the  following  current-time  curve,  the  readings 
taken  while  the  magnetic  field  was  present  being  marked  o,  and  those 
without  the  magnetic  field,  x.  It  is  apparent  that  all  lie  on  a  continuous 
curve  and,  therefore,  no  effect  can  be  noticed,  as  a  result  of  the  presence 
of  the  magnetic  field.  (Fig.  3.) 


FIG.  3. 


so 


7     • 

Time 


/Z, 


VARIATION  OF  CURRENT  WITH  VOLTAGE  AT  Low  PRESSURE. 

It  has  been  found  that  at  atmospheric  pressure  the  ratio  of  current 
to  potential  difference  between  plates  remains  constant  for  all  values 
of  the  potential  difference  between  ICO  volts  and  1000  volts,  thus 
showing  no  indication  of  a  saturation  current  within  that  range.  In 
order  to  ascertain  whether  this  remains  true  at  low  pressures,  the 


s 


potential  difference  was  varied  from  40  volts  to  600  volts  during  the 
cooling  of  quinine  at  15  mm.  pressure  with  the  following  results: 


Time. 

10  min. 

40  sec. 

11 

30 

12 

0 

12 

40 

14 

20 

15 

0 

16 

55 

17 

45 

19 

55 

23 

0 

Potential 
Current.   Difference. 


150 
300 

70 
200 
100 
180 

37 

60 
100 

35 


80 
600 

40 
200 

80 
600 

40 

80 
600 

80 


Time. 

25  min. 

10  sec. 

26 

10 

27 

.50 

29 

35 

30 

55 

33 

00 

33 

.50 

34 

35 

38 

45 

40 

0 

Potential 
Current.    Difference. 


60 
46 
46 
15 

5 

25 
30 

3 

20 
12 


600 

200 

600 

80 

40 

200 

600 

40 

600 

200 


By  plotting  four  curves  for  current-time  variations,  with  values  of 
potential  difference  of  CCO,  200,  80,  and  40  volts,  respectively,  the 
following  are  obtained : 


Voltage. 

600 

200 

80 

40 


The  results  on  a  current  voltage  diagram,  show  that  after  a  voltage 
of  about  180,  the  current  ceases  to  increase  with  voltage  at  its  original 
rate  and  gives  indication  of  a  saturation  value.  (Fig.  4.) 

FIG.  4. 


After 

12  min. 

After  17 

min. 

After 

23  min. 

Average 

Curent 

.     Ratio. 

Current. 

Ratio. 

Current 

.   Ratio. 

Ratio. 

272 

100 

144 

100 

76 

100 

100 

220 

80.8 

120 

83.3 

63 

82.8 

82.3 

130 

47.7 

69 

47.9 

35.0 

46.1 

47.2 

70 

25.7 

37 

25.7 

20.0 

26.3 

25.9 

Coo 


DIRECTION  OF  ELECTRIC  FIELD. 

No  ionization  current  could  be  detected  without  the  presence  of  an 
electric  field,  and  it  was  further  found  that  it  made  no  difference 
whether  the  quinine  plate  was  attached  to  the  battery  and  the  upper 


9 

plate  to  the  electroscope,  or  vice  versa,  providing  the  direction^ 
electric  field  remained  constant. 

As  regards  the  direction  of  the  field,  it  has  already  been  shown 
that  a  larger  current  is  produced  when  the  lower  plate  on  which  the 
quinine  rests,  is  the  positive  one.  This  would  seem  to  indicate 
that  the  phosphorescence  may  have  a  direct  influence  on  the  current. 
Observations  were  therefore  made  in  which  the  upper  plate  was  of 
different  materials  in  the  different  tests.  Lenard  has  shown  that  in 
such  cases  when  the  ionization  is  due  to  ultraviolet  light,  the  current 
is  greatest  when  the  light  falls  on  a  negatively  charged  zinc  plate;  but 
in  the  case  when  the  charging  is  due  to  the  quinine  radiations,  the 
intensity  of  the  ionization  was  found  to  remain  the  same,  whether  the 
upper  plate  was  of  zinc,  brass,  aluminum,  or  of  brass  covered  with 
lampblack.  The  accompanying  table  shows  these  values  obtained 
when  the  distance  between  the  plates  was  1.8  cm.  and  at  a  potential 
difference  of  200  volts.  An  upper  plate  with  its  surface  covered  with  a 
soap  film  was  also  found  not  to  alter  the  effect.  In  each  of  these  cases 
the  ratio  of  the  current  with  the  lower  plate  positive  to  that  with  it 
negative  remained  constant,  being  1.4  for  a  P.  D.  of  2CO  volts. 


Brass. 

Zinc. 

Lampblack. 

Time. 

Current. 

Time 

Current. 

Time. 

Current. 

1  min.  30  sec.    Began 

1 

min,  35 

sec.   Began 

1 

min.  30  sec. 

Began 

1           50 

60 

2 

00 

62 

2 

00 

60 

2           30 

80 

2 

52 

86 

2 

20 

75 

3           10 

75 

3 

22 

75 

3 

20 

75 

3           50 

65 

3 

47 

67 

3 

45 

60 

4           20 

45 

4 

30 

43 

4 

45 

40 

5           00 

35 

5 

45 

30 

o 

40 

30 

5           50 

29 

6 

30 

25 

6 

15 

27 

7           00 

23 

8 

45 

16 

7 

15 

22 

8   .       10 

19 

10 

22 

14.3 

8 

00 

17.50 

0          00 

14 

13 

15 

9.5 

10 

10 

12.50 

1           30 

11 

12 

00 

10 

That  there  is  no  ground  for  belief  that  the  ionization  is  directly  due 
to  ultraviolet  light  waves  was  further  proved  by  the  fact  that  pho- 
tographic plates  exposed  to  the  phosphorescent  light  after  the  latter 
had  passed  through  a  quartz  plate,  showed  no  difference  from  those 
obtained  when  the  quartz  was  replaced  by  glass  of  the  same  thickness. 
Observations  of  the  effect  of  cooling  in  damp  and  in  dry  air  at  atmos- 
spheric  pressure,  showed  that  both  the  ionization  and  the  phosphor- 
escence were  hastened  and  intensified  by  the  presence  of  damp  air. 
Unheated  quinine  which  had  been  kept  for  some  time  in  an  air-tight 
chamber  containing  phosphorus  pentoxide,  caused  ionization  and 
phosphorescence  as  soon  as  it  was  exposed  to  the  outside  air. 

The  results  so  far  obtained  seem  to  show  conclusively  that  since 
ionization  cannot  be  produced  or  altered  without  producing  or  altering 


10 


the  phosphorescence  and  since  the  latter  does  not  give  evidence  of 
ultraviolet  light  waves,  the  two  phenomena  are  taking  place  inde- 
pendently of  one  another,  but  are  produced  simultaneously  by  the 
same  cause  or  series  of  causes;  and  that  each  is  produced  during 


FIG.  5. 


/oo 
9o 
It 

7o 

It. 

O 
fo 

¥o 
3o 


/c 


•t— s 


(>      7      2       <}      ID     //     /z 

Time  in  minutes 


O  Brass       X  Zinc 


Lampblack 


hydration  and  dehydration  in  the  case  of  quinine  sulphate.  In  order 
to  ascertain  whether  either  effect  could  be  detected  during  the  forma- 
tion of  quinine  sulphate  from  its  alkaloid,  the  latter  was  sprinkled  over 
a  sheet  of  asbestos  soaked  with  sulphuric  acid  and  examined  in  the 
testing  chamber  and  also  in  a  dark  room,  but  neither  ionization  nor 


11 

phosphorescence  could  be  detected.  Observations  were  made  with 
quinine  mixed  with  quicklime,  with  salammoniac  and  with  the  sulphate 
of  sodium,  all  of  which  affect  the  solubility  of  the  sulphate  of  quinine 
in  water.  The  effects  in  each  case  were  not  different  from  those  which 
one  would  expect  if  mixed  with  any  inactive  matter. 


TESTS  WITH  OTHER  SUBSTANCES. 

Tests  similar  to  those  made  with  the  sulphate  of  quinine,  were  made 
with  many  of  the  more  common  substances  known  to  hydrate  easily, 
but  none  of  them  was  found  to  give  similar  effects.  Among  the  sub- 

FIG.  6. 


Quinine  Sulphate 


Anthracene 


Grape  Sugar 


Time 


12 

stances  tested  were  calcium  chloride,  calcium  sulphate,  zinc  sulphate 
and  copper  sulphate.  Other  substances  tested  for  other  reasons  were 
potassium  hydroxide,  sodium  hydroxide,  barium  oxide,  copper  nitrate, 
lead  nitrate,  grape  sugar,  aceto-acetic  ether,  fluorescine,  eosine,  anthra- 
cene, hydrocollidin-dicarboxylic  ether  and  sesculin.  Although  none  of 
these  gave  effects  comparable  in  magnitude  to  that  resulting  from  the 
sulphate  of  quinine;  sesculin,  grape  sugar,  and  anthracene  were  found 
to  produce  a  slight  ionization  of  the  surrounding  air  when  cooled  be- 
tween the  plates  of  a  condenser.  In  order  to  show  the  relative  effects 
produced  by  quinine  sulphate,  anthracene,  grape  sugar,  and  sesculin, 
equal  quantities  of  each  were  heated  to  the  same  temperature  (120° 
C.)  and  cooled  between  the  plates  of  a  small  condenser  with  an  air 
space  of  1  cm.  and  a  P.  D.  of  600  volts  between  the  plates.  Ionization 
curves  for  each  plotted  according  to  the  same  scale  are  given  side  by 
side  in  the  accompanying  diagram.  (Fig.  6.) 

The  effect  from  grape  sugar  like  that  from  the  sulphate  of  quinine 
might  be  attributed  to  hydration,  but  there  seems  to  be  no  reason  for 
attributing  the  anthracene  effect  to  that  cause.  Both  substances, 
however,  are  known  to  be  relatively  unstable  and  capable  of  presenting 
themselves  in  slightly  different  molecular  forms,  and  it  is  the  author's 
belief  that  the  effect  from  them  as  well  as  from  the  quinine,  is  due  to 
some  change  in  the  linkage  of  the  molecule  in  each  case.  This  varia- 
tion in  linkage  may  itself  persist  for  only  a  short  time,  after  which  the 
molecule  may  return  to  its  former  stable  condition,  and  thus  the 
effect  may  be  incapable  of  chemical  analysis;  but  it  may  nevertheless 
be  real  while  it  lasts  and  be  accompanied  by  a  temporary  ionization 
of  the  surrounding  gas. 


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